Go to Riot Support, submit all of the IT/internet files they can possibly want (they have a list on their support site here that you can reference), and ask them for help identifying any potential lag problems. More than likely they will be able to identify something other than Riot, and it's possibly something that you can remedy yourself.
Another possibility is that it wasn't Riot, but multiple people on the same ISP may have been affected due to either throttling or bottlenecking in the system. If you were playing with friends from your area who have the same type of internet from the same company, this is a greater possibility.
Yet another possibility is that one of the connections from an ISP to Riot's servers was severed, damaged, or otherwise disrupted. This would not affect everyone, but would possibly affect people from different ISPs depending on how their connection is done. When you run a traceroute (if you choose to submit a ticket), you'll see exactly how many steps that your connection to the servers goes through, and I think you'll be surprised by the number.
The alternative is you can come scream on the boards about how unfair it is that Riot, after explicitly saying in the Terms of Use that they are not liable for any service disruption due to technical issues, is unwilling to be liable for service disruption due to technical issues.